Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias, with an abnormally rapid rhythm being referred to as tachycardia. The present invention is concerned with the treatment of tachycardias which are frequently caused by the presence of an "arrhythmogenic region" or "accessory atrioventricular pathway" close to the inner surface of the chambers of a heart. The heart includes a number of normal pathways which are responsible for the propagation of electrical signals from upper to lower chamber necessary for performing normal function. The presence of arrhythmogenic region or accessory pathways can bypass or short circuit the normal pathways, potentially resulting in very rapid heart contractions, referred to here as tachycardias.
Cardiac mapping is used to locate aberrant electrical pathways and currents emanating within the heart. The aberrant pathways cause the contractions of the heart muscle to take on abnormal and life threatening dysrhythmias. Intracardiac mapping requires careful positioning of a plurality of catheters of multiple electrodes within the heart. For example, Webster, Jr. U.S. Pat No. 4,960,134 show the general use of a catheter, Desai U.S. Pat. No. 4,940,064 show the use of generally planar mapping arrays, Chilson U.S. Pat. No. 4,699,147 shows the use of a three dimensional basket mapping array, Houser U.S. Pat. No. 5,313,943 shows the use of a fluid flow conduit, and Imran U.S. Pat. No. 5,409,000 shows the use of ultrasonic markers of a basket array. It is important for a catheter or a catheter system to intimately contact the tissue for effective and time-saving mappings with minimum fluoroscopic exposure.
Treatment of tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying cause. Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. It is important for a clinician to be able to accurately steer the catheter to the region for ablation. Once at the region, it is important for a catheter to intimately contact the tissue to effectively control the emission of energy to ablate the tissue within the heart.
Regardless of the type of mapping means or ablation means used, the clinician is called upon to remotely move and manipulate the catheters in various ways. First, a catheter is inserted into a major vein or artery, usually in the neck or groin area. It is then guided into chambers of the heart by appropriate manipulation through the vein or artery. The distal tip section of a catheter must be manipulatable by a user from the proximal end of the catheter, so that the electrodes at the tip section can be positioned against the tissue region at the desired location to assure that all aberrant electrical pathways are mapped.
The development of prior mapping catheters has focused upon the requirements of in vitro mapping mechanisms. It requires the tip section including the electrodes as well as the catheter shaft to form a smooth continuous curve that may not intimately contact the non-smooth intracardiac tissue. The prior development has overlooked the important need to intimately contact the tissue by the electrodes, not the inter-electrode shaft itself, especially under the circumstances of the irregular intracardiac tissue contour. The intimate contacting of the electrodes alone of a catheter tip section via an inflatable tip shaft against the target tissue ensures effective cardiac mapping or ablation.